Juul was set to sell e-cigarettes at 1,400 Sainsbury's stores in the UK from November 4.

But it's not just underage smoking that poses a risk with e-cigarettes - a chemical found in some flavours have been linked to an irreversible lung condition.

Diacetyl, a chemical that creates a buttery flavour, has been linked to a condition called obliterative bronchiolitis, dubbed "popcorn lung" because of the high levels of disease found in workers from factories that used the chemical in microwave popcorn.

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Over time the inflammation associated with popcorn lung causes the tissues and airways in the organ to scar and narrow, leaving sufferers with breathing difficultiesCredit: Getty - Contributor

The condition causes causes inflammation, scarring and constriction of the bronchioles –the tubes through which air passes from your nose or mouth to your lungs.

Diacetyl is used in a number of buttery flavours like cupcake and candy floss.

Over time the inflammation associated with popcorn lung causes the tissues and airways in the organ to scar and narrow, leaving sufferers with breathing difficulties.

The symptoms may seem subtle to begin with, so can be easy to over look, they include; wheezing, a dry cough, shortness of breath, unexplained exhaustion, rapid breathing, persistent skin, eye or mouth irritation.

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Public Health England said the chemical diacetyl is banned in the UKCredit: Getty - Contributor

According to a Harvard University in 2016, Harvard University, there is a direct link between diacetyl in e-cigarettes and "popcorn lung".

The study tested 51 types of flavoured e-cigs – specifically choosing flavours that would be appealing to young people.

Out of the 51 flavours tested, 39 of them had above the recommended level of diacetyl, leading scientists to conclude that "urgent action is recommended to further evaluate this potentially widespread exposure via flavoured e-cigarettes".

A pamphlet released by the US Surgeon General's office also warned of the dangers of diacetyl in e-cigs, linking it to popcorn lung.

But the Harvard University analysis was done on e-cigarettes in the US, where diacetyl is allowed in vaping products.

In the UK the chemical is banned, so it's unlikely vapes you've bought here will contain the chemical.

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MPs have previously called for e-cigarettes to be free on the NHS as a stop smoking deviceCredit: Getty - Contributor

According to a Public Health England (PHE) blog, Public Health Matters, it's a "myth" that smoking e-cigarettes puts users at risk of popcorn lung.

But that doesn't mean flavours containing the chemical can't be bought online from the US.

"One of the most commonly held concerns is that e-cigarettes might cause popcorn lung," PHE said.

"This came about because some flavourings used in e-liquids to provide a buttery flavour contain the chemical diacetyl, which at very high levels of exposure has been associated with the serious lung disease bronchiolitis obliterans.

"The condition gained its popular name because it was initially observed among workers in a popcorn factory.

"However, diacetyl is banned as an ingredient from e-cigarettes and e-liquids in the UK.

"It had been detected in some e-liquid flavourings in the past, but at levels hundreds of times lower than in cigarette smoke. Even at these levels, smoking is not a major risk factor for this rare disease."

Cancer Research UK says so far there is "no good evidence" that vaping causes popcorn lung.

"Popcorn lung is a type of lung disease, but it is not cancer. Although popcorn lung is very rare, some e-cigarette users may worry about it," a statement on their website reads.

"In the UK, diacetyl was banned in e-cigarette liquid under the EU Tobacco Products Directive in 2016. So, e-liquids sold in the UK shouldn’t contain diacetyl.

"Current research finds that e-cigarettes are far less harmful than smoking and there’s growing evidence they may help some people to quit."

They want vaping to be more acceptable around the workplace with proper vaping policies for businesses and public places to be put in place in a bid to tackle "misunderstandings" about the practice

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